Just to expand on discussion we had earlier...

In my opinion, it is never going to be possible to make this crate as fast to compile as we want it to be, no matter what we throw at it, without taking a different approach. It's just tons of data, so using a codegen to generate tons of code and then asking rust to parse and compile it all is always going to take a long time.

A possible solution could be to pre-compile it as binary data. Something like this:

At build time:

• Convert JSON to HashMap/Vec/etc data structures.
• Serialize those data structures with rkyv.
• Save the serialized binary data to disk.

At runtime:

• Load the binary data from disk.
• Deserialize (which with rkyv is zero cost - just casting a pointer).
• Bonus points: Don't even load the data - just mmap it from disk.

Background: rkyv's "special sauce" is relative pointers: https://rkyv.org/architecture/relative-pointers.html